A bet­ter tool for anti-ic­ing emerges


Flying - - CONTENTS - By Les Abend

The vis­ual of large blue and green alu­minum frag­ments float­ing in the ice-laden Po­tomac River as we de­scended on our ap­proach into Wash­ing­ton Na­tional Air­port is still vivid enough to re­main locked in my mem­ory. The evening prior, Air Flor­ida Flight 90, a Boe­ing 737-200, had crashed into the 14th Street Bridge just af­ter take­off dur­ing a nasty snow­storm.

I re­mem­ber the date be­cause the ink hadn’t dried on my ATP cer­tifi­cate, my hav­ing passed the check ride only one day be­fore. The dra­mat­i­cally doc­u­mented ac­ci­dent oc­curred on Jan­uary 13, 1982. Al­though many other sig­nif­i­cant fac­tors con­trib­uted to the tragedy, the event be­came a water­shed mo­ment for the air­line in­dus­try, bring­ing in­creased aware­ness to the dan­gers of air­frame ic­ing.

Most of us un­der­stand that ic­ing de­forms the sur­face of the wing, se­ri­ously de­grad­ing lift-pro­duc­ing ca­pa­bil­ity. The de­gree to which the degra­da­tion oc­curs is de­pen­dent on many fac­tors that in­clude, but are not lim­ited to, the type of pre­cip­i­ta­tion, the in­ten­sity of the pre­cip­i­ta­tion, the out­side tem­per­a­ture and the shape of the air­foil.

Un­for­tu­nately, it wasn’t un­til just over 10 years af­ter the Air Flor­ida crash that de­ic­ing and anti-ic­ing op­er­a­tions were pro­foundly im­proved. The im­prove­ment came as a re­sult of the ac­ci­dent anal­y­sis of USAir Flight 405, a Fokker F28 that crashed shortly af­ter take­off from La Guardia’s Run­way 13 dur­ing a snow­storm on March 22, 1992. What was dis­cov­ered?

First, the Na­tional Trans­porta­tion Safety Board de­ter­mined that the Type I de­ic­ing fluid ap­plied to the F28 on two sep­a­rate oc­ca­sions be­fore taxi was not ca­pa­ble of con­tin­ued ic­ing pro­tec­tion for the con­di­tions present be­yond a few min­utes. It was cer­tainly com­pro­mised af­ter the 35 min­utes USAir Flight 405 spent on the ground. Type I fluid’s pur­pose is sim­ply to rid the air­plane of con­tam­i­nants as a de­icer, and has very lim­ited abil­ity as an anti-icer.

The so­lu­tion was a new fluid called Type IV, de­signed to be ap­plied af­ter Type I fluid. The Type IV mix­ture is con­sid­ered “anti-ice pro­tec­tion.” It has a much more ro­bust abil­ity to re­pel freez­ing pre­cip­i­ta­tion (e.g., snow). The fluid is also de­signed to shear off the wing as the air­plane ac­cel­er­ates dur­ing take­off with­out cre­at­ing an ap­pre­cia­ble ad­verse ef­fect on lift. The mix­ture is even­tu­ally com­pro­mised once it is sat­u­rated and can no longer ab­sorb freez­ing pre­cip­i­ta­tion. It has a time-lim­ited use­ful life de­pend­ing on the en­vi­ron­men­tal con­di­tions present. The use­ful life is called “holdover time.”

Holdover time is a sub­jec­tive in­ter­po­la­tion. Pi­lots are pro­vided charts within their oper-


ation man­u­als as to a time pe­riod for when the break­down of Type IV fluid oc­curs de­pend­ing on the form of pre­cip­i­ta­tion, pre­cip­i­ta­tion in­ten­sity and out­side tem­per­a­ture. If con­di­tions change (i.e., pre­cip­i­ta­tion in­ten­sity in­creases) the fi­nal au­thor­ity for when holdover time is ex­ceeded be­comes the de­ci­sion of the cap­tain. On av­er­age, holdover times are in min­utes, usu­ally less than an hour.

An­other im­prove­ment as a re­sult of USAir Flight 405 was the es­tab­lish­ment of ic­ing-fluid sta­tions strate­gi­cally lo­cated near the de­par­ture end of the ac­tive run­way rather than just at the gate area. This ic­ing “car wash” is or­ga­nized when weather con­di­tions war­rant it, the lo­ca­tion re­duc­ing the holdover time re­quired in freez­ing pre­cip­i­ta­tion. The de­icers them­selves are FAA-cer­ti­fied and are au­tho­rized to eval­u­ate the con­di­tion of the air­plane. At most ma­jor U.S. do­mes­tic air­ports, each air­line ar­ranges for a spe­cific ramp area, us­ing com­pany per­son­nel or con­tract per­son­nel to per­form the de­ic­ing/anti-ic­ing process.

Al­though the crew of USAir Flight 405 was cog­nizant of the po­ten­tial threat that the snow­storm pre­sented as they waited in line for take­off, their eval­u­a­tion of the air­plane con­di­tion was not ad­e­quate. The crew didn’t have the ap­pro­pri­ate pro­ce­dural eval­u­a­tion tools, nor did a lot of other air­lines, for that mat­ter. The cap­tain did have the flight de­iced with Type I fluid twice prior to taxi, but this was an eas­ier sit­u­a­tion, hav­ing the abil­ity to view the con­di­tion of the air­plane from out­side at the jet bridge.

For all car­ri­ers, an op­er­a­tional change was re­quired in the form of de­fin­i­tive pro­ce­dures for con­tam­i­na­tion eval­u­a­tion. I’m sim­pli­fy­ing the pro­ce­dure, but ba­si­cally, if holdover time is not ex­ceeded, then a cock­pit check of items such as the con­di­tion of wind­shield wipers is con­sid­ered. If the wipers have no ev­i­dence of frozen pre­cip­i­ta­tion, then the take­off can pro­ceed. If holdover time is ex­ceeded, then the air­plane has to be de­iced and anti-iced again. Or a cer­ti­fied de­icer can make the eval­u­a­tion. Or, in the ab­sence of a cer­ti­fied de­icer, a check is per­formed by a pi­lot from within the cabin be­cause it is of­ten dif­fi­cult, if not im­pos­si­ble, to see the wings from the cock­pit. Even with a cabin check, an eval­u­a­tion at night can be prob­lem­atic. (I speak from ex­pe­ri­ence, hav­ing at­tempted to view ac­cu­mu­la­tion on a B-757 wing dur­ing a night­time snow­storm at JFK.)

Fast-for­ward to present day and the same ba­sic pro­ce­dures re­main, al­beit with a lit­tle tweak­ing. But now, the pa­per holdover charts are used as a backup in­stead. In their place is an iPad ap­pli­ca­tion that al­lows us to en­ter all the per­ti­nent pa­ram­e­ters to de­ter­mine holdover time dur­ing any given freez­ing-pre­cip­i­ta­tion event for each fleet type. We can even set a timer to alert us as to the end of the holdover pe­riod. The ap­pli­ca­tion elim­i­nates much of the sub­jec­tive in­ter­po­la­tion of the pa­per charts, still leav­ing the fi­nal de­ci­sion to the cap­tain.

But alas, an even bet­ter mousetrap has been de­vel­oped. En­ter Vaisala, a cor­po­ra­tion with head­quar­ters in Fin­land and a main U.S. of­fice in Boul­der, Colorado. I spoke with Kevin Petty, the firm’s chief sci­ence of­fi­cer. Kevin has an im­pres­sive re­sume that in­cludes stints at the Na­tional Cen­ter for At­mo­spheric Re­search and the NTSB. One of the com­pany’s many me­te­o­ro­log­i­cal prod­ucts is called CheckTime, a de­ic­ing ap­pli­ca­tion that has been in de­vel­op­ment for ap­prox­i­mately five years.

Hav­ing agree­ments with var­i­ous air­port au­thor­i­ties through­out the world, Vaisala has been able to po­si­tion sen­sors that mea­sure a quan­tity called “liq­uid wa­ter equiv­a­lent” (LWE). What’s that? Imag­ine melt­ing a snow­ball. The wa­ter re­main­ing is LWE, a pa­ram­e­ter that de­ter­mines the ef­fec­tive­ness of any anti-ice fluid type for any given pre­cip­i­ta­tion con­di­tion. The sen­sors can eval­u­ate LWE ev­ery minute, con­tin­u­ally up­dat­ing holdover times even as pre­cip­i­ta­tion in­ten­sity varies.

The CheckTime sen­sors send a mes­sage to the cock­pit via ACARS or via in­ter­net con­nec­tiv­ity through an iPad app. The mes­sage is a con­tin­ual holdover-time up­date, an in­di­ca­tion of when the anti-ice fluid will fail. The tech­nol­ogy elim­i­nates al­most all of the guess­work, notwith­stand­ing that it helps to elim­i­nate can­celed flights and de­lays due to ad­di­tional anti-ic­ing ap­pli­ca­tions that would oth­er­wise be un­nec­es­sary. The cost sav­ings is in the thou­sands of dol­lars per air­line per event.

Kevin in­di­cated that Bos­ton, Chicago and Den­ver all have the tech­nol­ogy. Al­though he wouldn’t re­veal other car­ri­ers, Emi­rates air­line is one of the launch cus­tomers.

A phrase Kevin re­peated dur­ing our con­ver­sa­tion was “safety first through sci­ence.” I agree. It seems that sci­ence has cre­ated a bet­ter mousetrap that is bet­ter pre­pared to fight Mother Na­ture’s win­ter fury. Thank you, Vaisala.

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